Displacement measuring instrument

Abstract

A displacement measuring instrument (1) comprises: a light source (2); a first interferometer (10) to split a broadband source light (L11) into reference light (L13) and measuring light (L15) to cause the reference light (L13) to fall upon a reference surface (reference-side mirror 13) and the measuring light (L15) to fall upon a measuring surface (workpiece 9), and to superimpose the reference light (L13) and the measuring light (L15) to produce interference light (L16); a second interferometer (20) to split the interference light, causing the split interference light to strike a first reflective surface (first mirror 23) and a second reflective surface (second mirror 25), and to superimpose a first reflected light (L23, L26) and a second reflected light (L25, L27) to produce expanded light (L28) that expands in a predetermined expansion direction (E); an image sensor (3) to detect the expanded light (L28);and a processing device (4) to measure a displacement on the measuring surface based on a displacement of a peak position of an interference signal in an image detected by the image sensor (3).

Description

TECHNICAL AREA

[0001] The present invention relates to a displacement measuring instrument. STATE OF THE ART

[0002] Displacement measuring instruments that incorporate an interferometer using a light source configured to emit broadband light are known. Known examples of such displacement measuring instruments include a time-domain displacement measuring instrument, a spectral-domain displacement measuring instrument, and a wavelength-sweeping displacement measuring instrument.

[0003] The time-domain displacement measuring instrument mechanically changes an optical path length of a portion of an optical path of an interferometer and detects interference fringes generated at a portion where the difference in the length of the optical path between a reference light and a measurement light is zero, thereby measuring a displacement of a measurement target (see, for example, patent literature 1 (JP 2017-524138 A)).

[0004] The spectral-range displacement measuring instrument uses broadband light, such as white light, as a light source, causes the light to interfere using an interferometer, analyzes the resulting interference light spectrally to obtain frequency characteristics of the light intensity, and detects a peak position of an interference signal corresponding to a wavelength (see, for example, patent literature 2 (JP 2017-38997 A)).

[0005] The wavelength sweeping displacement measuring instrument sweeps (i.e. continuously changes) a wavelength of light emitted by a light source using an interferometer within a short time and detects a displacement of a measurement target based on frequency characteristics and phase of a change in light intensity caused to the interference light (see, for example, patent literature 3 (JP 2021-189112 A)).

[0006] The time-domain displacement measuring instrument, spectral-domain displacement measuring instrument and wavelength-sweeping displacement measuring instrument described above each have the following respective characteristics.

[0007] The time-domain displacement measuring instrument offers a relatively wide measurable range and high accuracy. On the other hand, the time-domain displacement measuring instrument requires mechanical operations to change the optical path length. These operations increase the time required for measurement, and mechanisms for precisely changing the optical path length, etc., incur high costs.

[0008] The spectral-range displacement measuring instrument requires no mechanical operation, yet offers high accuracy. However, the measurable range of the spectral-range displacement measuring instrument is very narrow, for example, 2 to 3 mm, and spectrometers and similar devices are expensive.

[0009] The wavelength sweep displacement measuring instrument requires no mechanical operations and allows for a relatively wide measuring range, for example, 1 m or more. However, it incurs high costs due to the use of a variable wavelength laser or similar technology and is also susceptible to temperature influences, making it difficult to achieve high accuracy.

[0010] As described above, it was difficult for existing linear encoders to simultaneously achieve high accuracy, a wide measurable range and low cost without requiring mechanical operations. SUMMARY OF THE INVENTION

[0011] One objective of the invention is to provide a displacement measuring instrument that can simultaneously achieve high accuracy, a wide measurable range and low cost without requiring mechanical operations.

[0012] According to one aspect of the invention, a displacement measuring instrument comprises: a light source configured to generate broadband source light; a first interferometer configured to split the source light into reference light and measurement light, to cause the reference light to fall upon a reference surface and the measurement light to fall upon a measurement surface, and to superimpose the reference light and the measurement light reflected from the reference surface and the measurement surface, respectively, to generate interference light;a second interferometer configured to split the interference light, causing the split interference light to strike a first reflective surface and a second reflective surface, and to superimpose a first reflected light reflected from the first reflective surface and a second reflected light reflected from the second reflective surface to produce expanded light that expands in a predetermined expansion direction and exhibits a change in an optical path length difference of the expanded light along the expansion direction; an image sensor configured to detect the expanded light; and a processing device configured to measure a displacement at the measurement surface based on a displacement of a peak position of an interference signal in an image detected by the image sensor.

[0013] According to the above aspect of the invention, a displacement measuring instrument can be provided which can simultaneously achieve high accuracy, a wide measurable range and low manufacturing costs without requiring mechanical operations. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 shows a layout plan representing an arrangement of a first exemplary embodiment of the invention. Fig. Figure 2 shows a schematic representation of an optical path length difference of expanded light generated by mirrors of the first exemplary embodiment. Fig. Figure 3 shows a schematic representation of a distance measurement of the first exemplary embodiment. Fig. Figure 4 shows a further schematic representation of a distance measurement of the first exemplary embodiment. Fig. Figure 5 shows a layout plan representing an arrangement of a second exemplary embodiment of the invention. Fig. Figure 6 shows a perspective view depicting a multi-stage inclined mirror of the second exemplary embodiment. Fig. Figure 7 shows a schematic representation of a distance measurement of the second exemplary embodiment. Fig. Figure 8 shows a schematic representation of a distance measurement of the second exemplary embodiment. Fig. Figure 9 shows a further schematic representation of a distance measurement of the second exemplary embodiment. Fig. Figure 10 shows a layout plan representing an arrangement of a third exemplary embodiment of the invention. Fig. Figure 11 shows a perspective view depicting a multi-stage inclined mirror of the third exemplary embodiment. Fig. Figure 12 shows a perspective view representing an aperture stop of the third exemplary embodiment. Fig. Figure 13 shows a perspective view depicting another aperture diaphragm of the third exemplary embodiment. Fig. Figure 14 shows a layout plan representing an arrangement of a fourth exemplary embodiment of the invention. Fig. Figure 15 shows a perspective view representing a cylindrical lens array of the fourth exemplary embodiment. Fig. Figure 16 shows a layout plan representing an arrangement of a fifth exemplary embodiment of the invention. Fig. Figure 17 shows a layout plan representing an arrangement of a sixth exemplary embodiment of the invention. Fig. Figure 18 shows a further schematic representation of a distance measurement of the sixth exemplary embodiment. Fig. Figure 19 shows a layout plan representing an arrangement of a seventh exemplary embodiment of the invention. Fig. Figure 20 shows a layout plan representing an arrangement of an eighth exemplary embodiment of the invention. DETAILED DESCRIPTION First exemplary embodiment

[0014] The Fig. 1, Fig. 2, Fig. 3 to Fig. Figure 4 each represents a displacement measuring instrument 1 of a first exemplary embodiment of the invention.

[0015] As in Fig. Figure 1 shows the displacement measuring instrument 1, which is set up to measure a displacement d9 of a workpiece 9, a light source 2, an image sensor 3, a processing device 4, a first interferometer 10 and a second interferometer 20.

[0016] The light source 2 is a light source device designed to generate a broadband source light L11 (e.g. white light).

[0017] The image sensor 3 is a one-dimensional or two-dimensional solid-state image sensor in the form of a charge-coupled (CCD) image sensor and the like.

[0018] The processing device 4, which is a computer system that can be operated according to a predetermined operating program, is set up to process images detected by the image sensor 3 and to calculate a displacement of the workpiece 9.

[0019] The first interferometer 10 comprises an incident-side lens 11, a beam splitter 12, a reference-side mirror 13 that defines a reference surface, and an emission-side lens 16. A surface of the workpiece 9 (measurement target) is defined as a measurement surface.

[0020] In the first interferometer 10, the source light L11 emitted by the light source 2 falls onto the incident-side lens 11 in order to be transmitted through it, and is split by the beam splitter 12 into a reference light L12 and a measuring light L14.

[0021] The reference light L12 is reflected by the reference-side mirror 13 in order to be returned as a reference light L13 to the beam splitter 12.

[0022] The measuring light L14 is reflected from the surface of the workpiece 9 (measuring surface) in order to be returned as a measuring light L15 to the beam splitter 12.

[0023] The reference light L13 and the measuring light L15, which were returned to the beam splitter 12, are superimposed to form interference light L16, which is emitted from the emission-side lens 16 to the second interferometer 20.

[0024] The second interferometer 20 comprises an incident-side lens 21, a beam splitter 22, a first mirror 23 defining a first reflective surface, a second mirror 25 defining a second reflective surface, and an emission-side lens 26.

[0025] The interference light L21 (L16) from the first interferometer 10 enters the incident-side lens 21. The interference light L21 transmitted through the incident-side lens 21, which is in the form of a beam with a predetermined optical path width, enters the beam splitter 22 to be split into a first split light L22 and a second split light L24.

[0026] The first split light L22 is reflected by the first mirror 23 in order to be returned as a first reflected light L23 to the beam splitter 22.

[0027] The second split light L24 is reflected by the second mirror 25 in order to be returned as a second reflected light L25 to the beam splitter 22.

[0028] The first mirror 23 and the second mirror 25 of the second interferometer 20 are designed as inclined mirrors, which are inclined with respect to the incident optical axes of the first split light L22 and the second split light L24 respectively.

[0029] The first mirror 23 is shifted in such a way that its left end is in Fig. 1 is shifted upwards, with the right end in Fig. 1 serves as a center. The first mirror 23 has a surface inclined at an angle θA with respect to a plane orthogonal to an incident optical axis of the first split light L22, with a displacement at the left end in Fig. 1 is defined as a distance dA. The first mirror 23, inclined in this way, generates an optical path length difference opdA, which is a distance 2dA between a component at the right end (in Fig. 1) and a component at the left end (in Fig. 1) of the first reflected light L23 with the predetermined optical path width and continuously changes from a distance of 0 to a distance of 2dA in the region from the right end to the left end. It should be noted that the optical path length difference opdA at the left end in Fig. 1, which is strictly represented by dA[1+cos(2θA)], can be approximated as the distance 2dA, since A is sufficiently small.

[0030] The second mirror 25 is shifted in such a way that its lower side is in Fig. 1 is shifted to the left, with the upper end in Fig. 1 serves as a center. The second mirror 25 has a surface inclined at an angle θB with respect to a plane orthogonal to an incident optical axis of the second split light L24, with a displacement on the lower side in Fig. 1 is defined as a distance dB. The second mirror 25, inclined in this way, creates an optical path length difference opdB, which represents a distance of 2dB between a component at the lower end (in Fig. 1) and a component at the upper end (in Fig. 1) of the second reflected light L25 with the predetermined optical path width and changes continuously between a distance of 0 and a distance of 2dB in the region between the upper and lower ends. It should be noted that the optical path length difference opdB at the lower end in Fig. 1, which is strictly represented by dB[1+cos(2θB)], as the distance can be approximated by 2dB, since θB is sufficiently small.

[0031] The first reflected light L23 and the second reflected light L25, which were returned to the beam splitter 22, are emitted by the emission-side lens 26 as a first reflected light L26 and a second reflected light L27 respectively to the image sensor 3.

[0032] The optical axes of the first reflected light L23 and the second reflected light L25 are each offset with respect to the optical axes of the original first split light L22 and second split light L24, such that the first reflected light L26 and the second reflected light L27 emitted by the beam splitter 22 do not overlap. The first reflected light L26 and the second reflected light L27 overlap when they incident on the surface of the image sensor 3 to form an expanded light L28 with a predetermined optical path width in an expansion direction E. The expanded light L28 expands in the predetermined expansion direction E. An optical path length difference opdC of the expanded light L28 varies along the expansion direction E.

[0033] Here, the propagation directions of the first reflected light L26 and the second reflected light L27 are inclined by 2θA and 2θB, respectively, with respect to the respective propagation directions of the reflected lights in a case where the first mirror 23 and the second mirror 25 have no inclinations, depending on the respective inclination angles θA and θB of the first mirror 23 and the second mirror 25. Therefore, as in Fig. Figure 2 shows that the first reflected light L26 and the second reflected light L27, which are superimposed to generate the expanded light L28, exhibit optical path length differences opdA and opdB of at most 2dA and 2dB on both sides in the expansion direction E, depending on the respective inclination angles 2θA and 2θB of the propagation directions of the first reflected light L26 and the second reflected light L27. Accordingly, the optical path length difference opdC generated in the expanded light L28, which is formed by superimposing the first and second reflected light L26 and L27, is equal to the sum of the optical path length differences opdA and opdB and varies continuously from a distance of 0 to a distance of 2dA + 2dB from one end to the other in the expansion direction E.The optical path length difference opdC of the expanded light L28 at a point that is a distance x away from one end in the expansion direction E is defined as a distance dCx (0 < dCx < 2dA + 2dB).

[0034] It should be noted that the inclination angles θA, θB of the first mirror 23 and the second mirror 25, and the distances 2dA, 2dB, defining the optical path length differences opdA, opdB, can each be the same value. It is not necessary for both the first mirror 23 and the second mirror 25 to be inclined; only one of the first and second mirrors 23, 25 can be inclined. In this case, the optical path length difference opdC of the expanded light L28 will be equal to the optical path length difference of the inclined mirror (i.e., one of the optical path length differences opdA, opdB).

[0035] As described above, the interference light L21 incident on the second interferometer 20 is the interference light L16 emitted by the first interferometer 10, and the interference light L16 contains an interference signal whose optical path length difference corresponds to twice the (round trip) displacement d9 on the surface of the workpiece 9, which is the measuring surface of the first interferometer 10.

[0036] Interference fringes are produced by the expanded light L28 when the optical path length difference opdC is twice as large as the displacement d9 on the surface of the workpiece 9. The optical path length difference opdC at this time is the distance dCx = 2d9, and therefore a point located a distance x away from the first end in the expansion direction E can be specified.

[0037] As in Fig. As shown in Figure 3, at most three peaks of the interference signal appear in the expanded light L28 detected by the image sensor 3. In the graph of Fig. 3 represents the vertical axis, the received optical signal intensity i detected by the image sensor 3, and the horizontal axis represents the distance x from a reference position in the expansion direction E.

[0038] When three peaks appear, a first peak p1 appears in the center, which is a peak of the interference signal, appearing at a point where the optical path length difference opdC of the second interferometer 20 is zero, constant at the same point regardless of the displacement d9 of the workpiece 9.

[0039] A second peak p2 and a third peak p3 appear at positions symmetrically to the left and right of the central first peak p1. The second peak p2 and the third peak p3 appear at positions where the total optical path length difference, which is a combination of an optical path length difference of the first interferometer 10 (corresponding to the displacement d9 of the workpiece 9) and an optical path length difference opdC of the second interferometer 20, becomes zero.

[0040] Both the distance xp between the first peak p1 and the second peak p2, and the distance between the first peak p1 and the third peak p3, are proportional to the optical path length difference of the first interferometer 10 (i.e., the displacement d9 of the workpiece 9). Accordingly, for example, the displacement d9 of the workpiece 9 can be calculated by measuring the distance xp between the first peak p1 and the second peak p2.

[0041] The position of the first peak p1, which is detected by the image sensor 3, can be selected by setting a relative position relationship between the first mirror 23 and the second mirror 25 or by adjusting the image sensor 3 and / or the computing unit 4.

[0042] Two peaks (i.e., the first peak p1 and the second peak p2) can be displayed during a measurement process by moving the position of the first peak p1 close to one end of a detectable area of ​​the image sensor 3, as shown in Fig. Figure 4 shows that such a setting makes it possible to observe the second peak p2 within the detectable range of the image sensor 3, even if the distance between the first peak p1 and the second peak p2 increases, so that the displacement d9 of the workpiece 9 can be measured over a wide range.

[0043] According to the exemplary embodiment, the following advantages can be achieved.

[0044] The displacement measuring instrument 1 of the exemplary embodiment comprises: the light source 2 for generating the broadband source light L11; the first interferometer 10 for splitting the source light into reference light L13 and measuring light L15, in order to cause the reference light L13 to fall on a reference surface (the reference-side mirror 13) and the measuring light L15 to fall on a measuring surface (the surface of the workpiece 9), and to measure the reference light L13 and the measuring light L15, which are emitted from the reference surface and the workpiece 9 respectively.to superimpose the light reflected from the measuring surface to generate interference light L16; the second interferometer 20 to split the interference light L21 (L16) to cause the split interference light L21 (L16) to incident on a first reflective surface (first mirror 23) and a second reflective surface (the second mirror 25), and to superimpose a first reflected light L23 reflected from the first reflective surface and a second reflected light L25 reflected from the second reflective surface to generate expanded light L28 which expands in a predetermined expansion direction E and exhibits a change in an optical path length difference opdC along the expansion direction E; the image sensor 3 to detect the expanded light L28; and the processing device 4 to measure the displacement d9 of the measuring surface (i.e.the surface of the workpiece 9) based on the displacement of the peak positions (the first peak p1 and the second peak p2) of the interference signal in the image detected by the image sensor 3.

[0045] According to the above arrangement, the interference light L16 (L21) emitted by the first interferometer 10 is transmitted through the second interferometer 20, in which peaks of the interference signal are generated in the expanded light L28 at a position where the optical path length difference opdC in the second interferometer 20 is equal to twice the displacement d9 of the workpiece 9, and these peaks are detected as interference peaks in the image of the expanded light L28.

[0046] More precisely, the expanded light L28 expands in the expansion direction E, and since the optical path length difference opdC varies along the expansion direction E with the distance dCx (0 < dCx < 2dA + 2dB), a peak of the interference signal is generated at a point x where the condition dCx 2d9 = 0 is satisfied. On the image expanded in the expansion direction E (see Fig. 3) The interference peaks (the first peak p1 and the second peak p2), which correspond to the optical path length difference opdC and the displacement d9, are reflected on the expanded light L28, and the displacement d9 of the workpiece 9 (measuring surface) can be measured with high accuracy based on the distance between the interference peaks on the image.

[0047] According to the above arrangement, since the interference peaks (the first peak p1 and the second peak p2) of the image of the expanded light L28 are measured, even signals that vary continuously along the expansion direction E can be measured in a single shot, and the mechanical operations and measurement time required as with existing time-domain displacement instruments are unnecessary. Furthermore, the measurable range can be increased by increasing the change in the distance dCx of the optical path length difference opdC of the expanded light L28 along the expansion direction E in the second interferometer 20.

[0048] According to the above arrangement, since the displacement d9 of the workpiece 9 (measuring surface) is measured based on the distance xp between the interference peaks (the first peak p1 and the second peak p2) on the image of the expanded light L28, a highly accurate measurement can be carried out stably, even in the presence of error factors (e.g. temperature change).

[0049] The position of the first peak p1 and the second peak p2, which are detected by the image sensor 3, can be adjusted by adjusting the relative position relationship between the first mirror 23 and the second mirror 25 or by adjusting the image sensor 3 and / or the computing unit 4.

[0050] At this point, if components of the displacement measuring instrument 1 are affected by the temperature change, the positions of the first peak p1 and the second peak p2, which are detected by the image sensor 3, may change. If the measurement is performed solely using position information from a single interference peak (e.g., the first peak p1 or the second peak p2), the measurement accuracy may be degraded by errors caused by the change in the position information. However, according to the displacement measuring instrument 1 of the exemplary embodiment, since the distance xp (i.e.,The relative shift between two interference peaks (the first peak p1 and the second peak p2) is used, canceling out the error components at the time of calculating the distance xp, even if the peaks change due to temperature or the like, so that a highly accurate measurement can be carried out constantly and stably.

[0051] The second interferometer 20 of the exemplary embodiment comprises the beam splitter 22 for splitting the interference light L21 in order to cause the interference light L21 to be incident on the first reflective surface (first mirror 23) and the second reflective surface (second mirror 25), wherein the first reflected light L26 (L23) and the second reflected light L27 (L25) are incident on the image sensor 3 via the beam splitter 22 and at least one of the first reflective surface (first mirror 23) or the second reflective surface (second mirror 25) is an inclined mirror arranged such that it is inclined in the expansion direction E with respect to the incident optical axis.

[0052] According to the above arrangement, the first interferometer 10 and the second interferometer 20 can each be implemented as a Twyman-Green interferometer. The inclined mirror, which defines one or both of the first reflective surface (first mirror 23) and the second reflective surface (second mirror 25), allows the optical path length difference opdA and / or opdB in the direction of the incident optical axis to be generated by the corresponding surface along the inclined direction. This makes it possible to generate the expanded light L28, which expands in the predetermined expansion direction E and exhibits a change in an optical path length difference opdC along the expansion direction E. Second exemplary embodiment

[0053] The Fig. 5, Fig. 6, Fig. 7, Fig. 8 to Fig. Figure 9 each represents a displacement measuring instrument 1A of a second exemplary embodiment of the invention.

[0054] Some of the components of the exemplary embodiment differ from those of the first exemplary embodiment described above. The components common to both exemplary embodiments are omitted, and the differing component(s) are described below.

[0055] As in Fig. Figure 5 comprises a displacement measuring instrument 1A, which is set up to measure the displacement d9 of the workpiece 9, the light source 2, the image sensor 3, the processing device 4, the first interferometer 10 and a second interferometer 20A.

[0056] In the first exemplary embodiment described above, the first mirror 23, which is arranged so that it is inclined, is used as the first reflective surface of the second interferometer 20 (see Fig. 1) In contrast, the second interferometer 20A of the exemplary embodiment uses a multi-stage inclined mirror 23A as the first reflective surface.

[0057] It should be noted that the second mirror 25, which serves as the second reflecting surface of the second interferometer 20A, is assumed herein to be untilted for the sake of simplicity (i.e. angle θB = 0), satisfying the optical path length difference opdC = opdA.

[0058] As in Fig. As shown in Figure 6, the multi-stage inclined mirror 23A is provided by cutting a part of a rectangular parallelepipedic base 230 to form steps (inclined surfaces 231 to 234) and by precisely polishing the surfaces to form an inclined mirror with high flatness.

[0059] The inclined surfaces 231 to 234 are each inclined by an angle θA with respect to a virtual reference surface 239, which is offset by a predetermined distance from a rear surface of the base 230. Due to this inclination, the inclined surfaces 231 to 234 have distances from the reference surface 239 of the respective surfaces that increase from one end (on the left side of the drawing) to the other end (on the right side of the drawing) and reach a maximum change distance dA. The inclined surfaces 231 to 234 are each offset in steps by the distance dA.

[0060] The multi-stage inclined mirror 23A is installed such that the reference surface 239 is aligned with a plane orthogonal to the incident optical axis of the first split light L22. Each of the inclined surfaces 231 to 234 thus serves as a similar inclined mirror corresponding to the first mirror 23 of the first exemplary embodiment described above.

[0061] The offset distance dA of each of the inclined surfaces 231 to 234 is the same as the maximum distance dA (change magnitude) of the inclined mirror. Accordingly, the change magnitude of the first split light L22 in the direction of the incident optical axis can be expanded from the distance dA (change magnitude per surface) to the distance 4dA (change magnitude of a total of four surfaces) by virtually connecting the inclined surfaces 231 to 234 sequentially.More precisely, if the left end (in the drawing) of the inclined surface 231 is set to 0 for the change in the direction of the incident optical axis of the first split light L22, the right end (in the drawing) of the inclined surface 231 is at a distance dA, the left end (in the drawing) of the inclined surface 232 is at the same distance dA as the right end (in the drawing) of the inclined surface 231, and the right end (in the drawing) of the inclined surface 232 is at a distance of 2dA. Similarly, by accumulating in this way, the right end (in the drawing) of the inclined surface 234 becomes at a distance of 4dA.

[0062] Accordingly, when the first split light L22 falls on the multi-stage inclined mirror 23A, the optical path length can be changed in a range from 0 to at most the distance 8dA (twice the maximum distance 4dA in the direction of the incident optical axis), depending on the position of incidence on the entire surface composed of the inclined surfaces 231 to 234.

[0063] Returning to Fig. 5 The first reflected light L26 passes through the multi-stage inclined mirror 23A onto the image sensor 3, where it is superimposed on the second reflected light L27 from the second mirror 25 to form the expanded light L28. In this case, if the image sensor 3 is configured as a two-dimensional image sensor, four stripes of the expanded light L28, corresponding to the four stripes of the first reflected light L26 reflected from the inclined surfaces 231 to 234, are detectable in the image.

[0064] As in the Fig. 7, Fig. 8 to Fig. As shown in Figure 9, the four stripes of expanded light L28, which was reflected from the inclined surfaces 231 to 234, are detected by the image sensor 3.

[0065] More precisely, the inclined surfaces 231 to 234 of the multi-stage inclined mirror 23A are each arranged in a direction that intersects the respective inclined directions and the incident optical axis of the first split light L22. Accordingly, the first reflected light L26, which occurs from the inclined surfaces 231 to 234 onto the image sensor 3, forms four parallel stripes extending in the inclined directions of the respective inclined surfaces 231 to 234. Since the second reflected light L27 is uniformly distributed over the entire surface of the image sensor 3, the expanded light L28, which is generated in an overlap region with the first reflected light L26, also appears in the form of four stripes corresponding to the first reflected light L26.

[0066] As described above, the optical path length generated by the inclined surfaces 231 to 234 changes in a range from 0 to a maximum distance of 8 dA by sequentially connecting the images formed by the surfaces. Accordingly, the optical path length difference opdC of the expanded light L28 can be increased from 0 to a maximum distance of 8 dA by sequentially connecting the four strips of expanded light L28 detected by the image sensor 3 and bringing the first peak p1 close to the left end (0 position) in the drawing.

[0067] As in Fig. As shown in Figure 7, when the optical path length difference opdC of the expanded light L28 is in the range of 0 to 2dA, the peaks (the first peak p1 and the second peak p2) of the interference signal appear on the uppermost fring of the expanded light L28.

[0068] If the optical path length difference opdC of the expanded light L28 is in the range exceeding 2dA to 4dA, the second peak p2 appears on the second fring of the expanded light L28.

[0069] Accordingly, the displacement d9 of the workpiece 9 can be calculated by measuring the distance xp between the first peak p1 and the second peak p2, as in the first exemplary embodiment described above.

[0070] As in Fig. Figure 8 shows that when the optical path length difference opdC of the expanded light L28 exceeds the distance 2dA, although the first peak p1 remains in the same position, the second peak p2 appears on the second strip of the expanded light L28.

[0071] In Fig. 8 is defined as a distance xp1 from the first peak p1 to a point where the optical path length difference opdC on the uppermost fring of the expanded light L28 reaches a distance of 2dA, and as a distance xp2 from the point located at a distance of 2dA on the second fring of the expanded light L28 to the second peak p2. The distance from the first peak p1 to the second peak p2 can be calculated using the formula: distance xp = xp1 + xp2, where the displacement d9 of the workpiece 9 can be calculated based on the calculated distance xp.

[0072] Similarly, if the optical path length difference opdC of the expanded light L28 exceeds the distance 4dA, although the first peak p1 remains in the same position, the second peak p2 appears on the third strip of the expanded light L28.

[0073] Furthermore, if the optical path length difference opdC of the expanded light L28 exceeds the distance 6dA, although the first peak p1 remains in the same position, the second peak p2 appears on the fourth fring of the expanded light L28.

[0074] It will be in Fig. 9. Assume that a distance from the first peak p1 to a point where the optical path difference opdC on the uppermost strip of the expanded light L28 reaches a distance of 2dA is the distance xp1, a distance from the point where the optical path difference opdC on the second strip of the expanded light L28 reaches a distance of 2dA to a point where the optical path difference opdC reaches a distance of 4dA is the distance xp2, a distance from the point where the optical path difference opdC on the third strip of the expanded light L28 reaches a distance of 4dA to a point where the optical path difference opdC reaches a distance of 6dA is the distance xp3, and a distance from the point where the optical path difference opdC on the fourth strip of the expanded light L28 reaches a distance of 6dA to the second peak p2 is the distance xp4.Here, the distance from the first peak p1 to the second peak p2 can be calculated using a formula: distance xp = xp1 + xp2 + xp3 + xp4, where the displacement d9 of the workpiece 9 can be calculated based on the calculated distance xp.

[0075] Accordingly, even if the peak positions (the first peak p1 and the second peak p2) of the interference signal detected in the expanded light L28 are far apart and cannot be covered by the single inclined mirror (each of the inclined surfaces 231 to 234), the peak positions can be detected by connecting the plurality of strips, so that the measurable area of ​​the expanded light L28 can be increased.

[0076] It should be noted that the second mirror 25, which serves as the second reflecting surface of the second interferometer 20A and is assumed above to be uninclined for simplification (i.e., angle θB = 0), is optionally inclined by the angle θB, as in the first exemplary embodiment. In this case, in the multi-stage inclined mirror 23A, although the inclined surfaces 231 to 234 are each offset stepwise by distances dA, the optical path length difference opdC of the second interferometer 20A can be changed from 0 to the maximum distance of 8(dA + dB) by changing the distance dA to (dA + dB).

[0077] According to the exemplary embodiment, the following advantage can be achieved in addition to the same advantages as in the first exemplary embodiment described above.

[0078] In the exemplary embodiment, the inclined mirror is the multi-stage inclined mirror 23A, which comprises a plurality of inclined mirrors (the inclined surfaces 231 to 234) arranged in a direction that intersects the incident optical axis and the expansion direction (the inclined direction), wherein the plurality of inclined mirrors are offset in the direction of the incident optical axis.

[0079] According to the above arrangement, by sequentially shifting the inclined mirrors (the inclined surfaces 231 to 234) at the respective stages in the direction of the optical axis, the optical path length difference opdC in the direction of the optical axis can be increased as an entirety of the multi-stage inclined mirror 23A, so that a wide measurable range can be achieved which cannot be obtained by a single inclined mirror. Third exemplary embodiment

[0080] The Fig. 10, Fig. 11, Fig. 12 to Fig. 13 each represent a displacement measuring instrument 1B of a third exemplary embodiment of the invention.

[0081] Some of the components of the exemplary embodiment differ from those of the first exemplary embodiment described above. The components common to both exemplary embodiments are omitted, and the differing component(s) are described below.

[0082] As in Fig. Figure 10 shows the displacement measuring instrument 1B, which is set up to measure the displacement d9 of the workpiece 9, the light source 2, the image sensor 3, the processing device 4, the first interferometer 10 and a second interferometer 20B.

[0083] In the first exemplary embodiment described above, the first mirror 23, which is arranged so that it is inclined, is used as the first reflective surface of the second interferometer 20 (see Fig. 1) In contrast, the second interferometer 20B of the exemplary embodiment uses a multi-stage inclined mirror 23B as the first reflective surface. It should be noted that the second reflective surface of the second interferometer 20B of the exemplary embodiment is also defined as the inclined second mirror 25, as in the first exemplary embodiment described above.

[0084] As in Fig. As shown in Figure 11, the multi-stage inclined mirror 23B is provided by cutting a part of the rectangular parallelepipedic base 230 to form steps (inclined surfaces 231 to 238) and by precisely polishing the surfaces to form inclined mirrors with high flatness.

[0085] While the multi-stage inclined mirror 23A (see Fig. 6) Whereas the second exemplary embodiment described above has four stages of inclined mirrors (the inclined surfaces 231 to 234), the multi-stage inclined mirror 23B of the exemplary embodiment has an increased number of stages, and the inclined mirrors (inclined surfaces 231 to 238) are provided in eight stages. The structure of the multi-stage inclined mirror 23B of the exemplary embodiment is the same as that of the multi-stage inclined mirror 23A of the second exemplary embodiment, except for the increased number of stages.

[0086] Returning to Fig. 10. The displacement measuring instrument 1B, whose multi-stage inclined mirror 23B has a larger number of inclined mirror stages than the displacement measuring instrument 1A of the second exemplary embodiment, can further increase the measurable range.

[0087] When the number of inclined mirror stages is increased, as in the multi-stage inclined mirror 23B, the reflected light from the respective inclined mirror stages is significantly affected by diffraction, sometimes causing defects in the image projected onto the image sensor 3. To prevent this disadvantage, the displacement measuring instrument 1B is equipped with an aperture diaphragm 27B in the form of two holes (see Fig. 12) or a slot (see Fig. 13) between the image sensor 3 and the beam splitter 22.

[0088] The in Fig. Aperture 27B, as shown in Figure 12, has two circular holes 271 arranged along the expansion direction E. The first reflected light L26 and the second reflected light L27 are each transmitted through a corresponding circular hole 271 to incident on the image sensor 3 in a limited state.

[0089] The in Fig. The aperture diaphragm 27B shown in Figure 13 has a slit 272 extending along the expansion direction E. The first reflected light L26 and the second reflected light L27 are transmitted through the slit 272 to incident on the image sensor 3 in a limited state.

[0090] According to the exemplary embodiment, the following advantage can be achieved in addition to the same advantages as in the first and second exemplary embodiments described above.

[0091] In the exemplary embodiment, the aperture diaphragm 27B is installed between the image sensor 3 and the beam splitter 22 to regulate the first reflected light L26 and the second reflected light L27.

[0092] According to the above arrangement, a large depth of field can be achieved by blocking the diffraction light originating from the structure of the multi-stage inclined mirror 23B, so that the reflected light from the multi-stage inclined mirror 23B, which has a large depth in the direction of the optical axis, can be clearly imaged, thereby achieving a larger measurable area. Fourth exemplary embodiment

[0093] Fig. 14 to Fig. 15 each represent a displacement measuring instrument 1C of a fourth exemplary embodiment of the invention.

[0094] Some of the components of the exemplary embodiment differ from those of the first exemplary embodiment described above. The components common to both exemplary embodiments are omitted, and the differing component(s) are described below.

[0095] As in Fig. Figure 14 shows the displacement measuring instrument 1C, which is set up to measure the displacement d9 of the workpiece 9, the light source 2, the image sensor 3, the processing device 4, the first interferometer 10 and a second interferometer 20C.

[0096] In the first exemplary embodiment described above, the first mirror 23, which is arranged so that it is inclined, is used as the first reflective surface of the second interferometer 20 (see Fig. 1) In contrast, the second interferometer 20C of the exemplary embodiment uses the multi-stage inclined mirror 23A (as in the second exemplary embodiment described above) to define the first reflective surface. It should be noted that the second reflective surface of the second interferometer 20C of the exemplary embodiment is also defined as the inclined second mirror 25, as in the first exemplary embodiment described above.

[0097] The displacement measuring instrument 1C is further equipped with a cylindrical lens array 28C between the image sensor 3 and the beam splitter 22.

[0098] As in Fig. As shown in Figure 15, the cylindrical lens array 28C comprises four cylindrical lenses 281 arranged parallel along the expansion direction E. Each of the cylindrical lenses 281 condenses the first reflected light L26 from a corresponding inclined mirror in four stages (inclined surfaces 231 to 234) of the multi-stage inclined mirror 23A, thereby forming, together with the second reflected light L27 from the second mirror 25, four stripes of expanded light L28 extending along the expansion direction E on the surface of the image sensor 3.

[0099] Due to the presence of the cylindrical lens array 28C, the amount of light received by the image sensor 3 per unit area can be increased to enhance the light intensity of the expanded light L28.

[0100] According to the exemplary embodiment, the following advantage can be achieved in addition to the same advantages as in the first and second exemplary embodiments described above.

[0101] The cylindrical lenses 281 (the cylindrical lens array 28C), which are continuous in the expansion direction E and condense the incident light (the first reflected light L26 and the second reflected light L27) onto the image sensor 3, are provided in the exemplary embodiment.

[0102] According to the above arrangement, the incident light (the first reflected light L26 and the second reflected light L27) is condensed to increase the light intensity when it is received by the image sensor 3. Additionally, by using the cylindrical lenses 281, which are continuous in the expansion direction E, it is possible to ensure properties of the expanded light L28 that are necessary for the measurement (i.e., expansion in the predetermined expansion direction E and exhibiting a change in the optical path length difference opdC along the expansion direction E). Fifth exemplary embodiment

[0103] Fig. 16 represents a displacement measuring instrument 1D of a fifth exemplary embodiment of the invention.

[0104] Some of the components of the exemplary embodiment differ from those of the first exemplary embodiment described above. The components common to both exemplary embodiments are omitted, and the differing component(s) are described below.

[0105] As in Fig. Figure 16 shows the displacement measuring instrument 1D, which is set up to measure the displacement d9 of the workpiece 9, the light source 2, the image sensor 3, the processing device 4, the first interferometer 10 and a second interferometer 20D.

[0106] In the first exemplary embodiment described above, the first reflective surface and the second reflective surface of the second interferometer 20 are the first mirror 23 and the second mirror 25, respectively, which are substantially orthogonal to and slightly inclined with respect to the first split light L22 and the second split light L24 from the beam splitter 22, wherein the first reflected light L23 and the second reflected light L25 are returned to the beam splitter 22 to form the second interferometer 20 in the form of a Twyman-Green interferometer (see Fig. 1).

[0107] In contrast, the second interferometer 20D of the exemplary embodiment is a two-beam, one-way interferometer similar to a Mach-Zehnder interferometer. However, it should be noted that although the beams from two optical paths are superimposed by a beam splitter installed in front of the image sensor in the Mach-Zehnder interferometer, the beam splitter is omitted in the second interferometer 20D of the exemplary embodiment, and the beams are superimposed on the image sensor 3.

[0108] More precisely, the second interferometer 20D of the exemplary embodiment comprises a first mirror 23D and a second mirror 25D, which are strongly inclined with respect to the first split light L22 and the second split light L24. The first mirror 23D and the second mirror 25D emit the first reflected light L23 and the second reflected light L25, respectively, in a direction opposite to the beam splitter 22, so that the lights are superimposed on the image sensor 3 to generate the expanded light L28.

[0109] In the second interferometer 20D, the first reflected light L23 and the second reflected light L25, which are to be incident on the image sensor 3, are converted into beams that expand in the expansion direction E by appropriately controlling the tilt angles of the first mirror 23D and the second mirror 25D. The optical path lengths of the first reflected light L23 and the second reflected light L25 are the same. In contrast, the angle of incidence of the first reflected light L23 on the image sensor 3 is defined such that it differs from the angle of incidence of the second reflected light L25 on the image sensor 3.

[0110] By superimposing the first reflected light L23 and the second reflected light L25 onto each other, the expanded light L28 is generated, similar to that in the first exemplary embodiment described above. The interference signal (see Fig. 3) of the expanded light L28 is measured in the same way as described in the first exemplary embodiment, which makes it possible to measure the displacement d9 of the workpiece 9 (measurement target).

[0111] Accordingly, even with the displacement measuring device 1D of the exemplary embodiment, the same advantages can be achieved as in the first exemplary embodiment described above, and the following advantage can also be achieved.

[0112] The second interferometer 20D of the exemplary embodiment comprises the beam splitter 22 for splitting the interference light L21 to cause the interference light L21 to incident on the first reflective surface (first mirror 23D) and the second reflective surface (second mirror 25D). The first reflected light L23 and the second reflected light L25 incident on the image sensor 3 without passing through the beam splitter 22, the angle of incidence of the first reflected light L23 on the image sensor 3 differing from the angle of incidence of the second reflected light L25 on the image sensor 3.

[0113] According to the above arrangement, the first interferometer 10 is provided by a Twyman-Green interferometer, and the second interferometer 20D is provided by a dual-beam, one-way interferometer similar to a Mach-Zehnder interferometer. Using the dual-beam, one-way interferometer, whose optical path is simpler than that of the Twyman-Green interferometer, the loss in the amount of light reaching the image sensor 3 can be reduced.

[0114] In the second interferometer 20D, a continuous optical path length difference opdC can be generated on the expanded light L28, which is produced on the surface of the image sensor 3, by making the angles of incidence of the first reflected light L23 and the second reflected light L25 on the image sensor 3 different. In this case, by shaping the image sensor 3 so that it is long in the expansion direction E, the optical path length difference opdC in the expanded light L28 can be increased, thereby extending the measurement range.

[0115] Furthermore, by using a one-dimensional sensor extending in the expansion direction E, as the image sensor 3, the measurement operation can be further accelerated. Sixth exemplary embodiment

[0116] Fig. 17 represents a displacement measuring instrument 1E of a sixth exemplary embodiment of the invention.

[0117] Some of the components of the exemplary embodiment differ from those of the fifth exemplary embodiment described above. The components common to both exemplary embodiments are omitted, and the differing component(s) are described below.

[0118] As in Fig. Figure 17 shows the displacement measuring instrument 1E, which is set up to measure the displacement d9 of the workpiece 9, the light source 2, the image sensor 3, the processing device 4, the first interferometer 10 and a second interferometer 20E.

[0119] The second interferometer 20E of the exemplary embodiment has a structure similar to that of the second interferometer 20D (see Fig. 16) of the fifth exemplary embodiment described above. However, it should be noted that in the exemplary embodiment, a second mirror 25E is arranged further away from the beam splitter 22 compared to the second mirror 25D of the fifth exemplary embodiment, thereby increasing the optical path length of the second reflected light L25.

[0120] According to the displacement measuring instrument 1E of the exemplary embodiment, as described for the displacement measuring instrument 1D in the fifth exemplary embodiment, the displacement d9 of the workpiece 9 (measuring target) can be measured by measuring the interference signal of the expanded light L28 received by the image sensor 3, as in the displacement measuring instrument 1 of the first exemplary embodiment described above.

[0121] Furthermore, according to the displacement measuring instrument 1E of the exemplary embodiment, a projected position of the expanded light L28, which is received by the image sensor 3, can be shifted by changing the position of the second mirror 25E in order to lengthen the optical path of the second reflected light L25.

[0122] As shown in an upper diagram in Fig. As shown in Figure 18, if the displacement d9 of the workpiece 9 is large, the interval between the interference signals in the expanded light L28 obtained by the displacement measuring device 1D of the fifth embodiment becomes wide and may not fit within the width of the image sensor 3. According to the displacement measuring instrument 1E of the exemplary embodiment, the projected position of the expanded light L28 on the image sensor 3 can be shifted, as shown in a lower diagram in Figure 18. Fig. 18 shows that even if the interval between the interference signals (i.e. the distance xp between the first peak p1 and the second peak p2) is wide, this can be detected in a single shot by the image sensor 3.

[0123] In the second interferometer 20E of the exemplary embodiment, the optical path length from the beam splitter 22 to the image sensor 3 via the first reflective surface (the first mirror 23D) and the optical path length from the beam splitter 22 to the image sensor 3 via the second reflective surface (the second mirror 25E) are different from each other.

[0124] According to the above arrangement, the peaks of the interference fring appearing on the expanded light L28 received by the image sensor 3 can be shifted in the expansion direction E (i.e., the direction in which the image sensor 3 is elongated) by adjusting the positions of the first reflective surface (the first mirror 23D) and the second reflective surface (the second mirror 25E) (i.e., changing the position of the second mirror 25E) to create a difference in the optical path length of the reflected light between the first and second reflective surfaces. For example, by shifting an interference signal peak (the first peak p1), which serves as a reference indicating that the optical path difference opdC of the second interferometer 20 is zero, to one end of a light-receiving region, a longer measurement width of the optical path difference can be created, and the measurement range can be extended. Seventh exemplary embodiment

[0125] Fig. 19 represents a displacement measuring instrument 1F of a seventh exemplary embodiment of the invention.

[0126] Some of the components of the exemplary embodiment differ from those of the fifth exemplary embodiment described above. The components common to both exemplary embodiments are omitted, and the differing component(s) are described below.

[0127] As in Fig. Figure 19 shows the displacement measuring instrument 1F, which is set up to measure the displacement d9 of the workpiece 9, the light source 2, the image sensor 3, the processing device 4, the first interferometer 10 and a second interferometer 20F.

[0128] The second interferometer 20F of the exemplary embodiment has a structure similar to that of the second interferometer 20E (see Fig. 17) of the sixth exemplary embodiment described above. In addition, a cylindrical lens 28F is installed along the light-receiving surface of the image sensor 3 in the exemplary embodiment.

[0129] According to the exemplary embodiment, the following advantage can be achieved in addition to the same advantages as in the fifth and sixth exemplary embodiments described above.

[0130] The cylindrical lens 28F, which is continuous in the expansion direction E and condenses the incident light (the first reflected light L23 and the second reflected light L25) onto the image sensor 3, is provided in the exemplary embodiment.

[0131] According to the above arrangement, the incident light (the first reflected light L23 and the second reflected light L25) is condensed to increase the light intensity when it is received by the image sensor 3. Additionally, by using the cylindrical lens 28F, which is continuous in the expansion direction E, it is possible to ensure properties of the expanded light L28 that are necessary for the measurement (i.e., expansion in the predetermined expansion direction E and exhibiting a change in the optical path length difference opdC along the expansion direction E). Eighth exemplary embodiment

[0132] Fig. 20 represents a displacement measuring instrument 1G of an eighth exemplary embodiment of the invention.

[0133] Some of the components of the exemplary embodiment differ from those of the second exemplary embodiment described above. The components common to both exemplary embodiments are omitted, and the differing component(s) are described below.

[0134] As in Fig. Figure 20 shows the displacement measuring instrument 1G, which is configured to measure the displacement d9 of the workpiece 9, comprising the light source 2, the image sensor 3, the processing device 4, a first interferometer 10G and the second interferometer 20A. Among the above, the light source 2, the image sensor 3, the processing device 4 and the second interferometer 20A are the same as those in the second exemplary embodiment described above.

[0135] In the displacement measuring instrument 1G of the exemplary embodiment, the path from the light source 2 to the first interferometer 10G and the path from the first interferometer 10G to the image sensor 3 are provided by optical fibers 31, 32, 33 and a coupler 34.

[0136] The first interferometer 10G comprises the incident-side lens 11, the beam splitter 12, and the reference-side mirror 13, which defines the reference surface. One surface of the workpiece 9 (measurement target) is defined as a measurement surface.

[0137] In the first interferometer 10G, the source light L11 emitted by the light source 2 passes through the optical fibers 31, 32 onto the incident-side lens 11 to be transmitted through it, and the source light L11 is split by the beam splitter 12 into the reference light L12 and the measuring light L14.

[0138] The reference light L12 is reflected by the reference-side mirror 13 in order to be returned as a reference light L13 to the beam splitter 12.

[0139] The measuring light L14 is reflected from the surface of the workpiece 9 (measuring surface) in order to be returned as a measuring light L15 to the beam splitter 12.

[0140] The reference light L13 and the measurement light L15, which were returned to the beam splitter 12, are superimposed to form interference light L16. The interference light L16 is transmitted again through the incident-side lens 11 and then emitted through the optical fibers 32, 33 to the second interferometer 20A.

[0141] As described in the second exemplary embodiment, the emitted interference light L16 is detected as the expanded light L28 by the second interferometer 20A through the image sensor 3, thereby measuring the displacement d9 of the workpiece 9.

[0142] In the first interferometer 10G of the exemplary embodiment, the entry of the source light L11 and the exit of the interference light L16 are at the same location, the path of the source light L11 from the light source 2 to the first interferometer 10G (the optical fibers 31, 32) and the path of the interference light L16 from the first interferometer 10G to the second interferometer 20A (the optical fibers 32, 33) are provided by the optical fibers 31, 32, 33, and parts of the optical fibers near the first interferometer 10G (the optical fiber 32) are combined into a single fiber.

[0143] According to the above arrangement, the first interferometer 10G and the workpiece 9 can be arranged remotely from the light source 2 and the second interferometer 20A, so that the size of a probe incorporating the first interferometer 10G can be reduced, making it possible to easily insert the probe even if the workpiece 9 is located in a narrow gap or the like. Additional explanation

[0144] The following additional explanation regarding the exemplary embodiments described above is given below. Additional Explanation 1

[0145] A distance measuring instrument, comprehensive: a light source designed to produce broadband source light; a first interferometer, which is set up to split the source light into reference light and measurement light, to cause the reference light to fall on a reference surface and the measurement light to fall on a measurement surface, and the reference light and the measurement light that are emitted from the reference surface and the measurement light respectively.to superimpose the light reflected from the measuring surface to produce interference light; a second interferometer, configured to split the interference light, to cause the split interference light to strike a first reflective surface and a second reflective surface, and to superimpose a first reflected light reflected from the first reflective surface and a second reflected light reflected from the second reflective surface to produce expanded light that expands in a predetermined expansion direction and exhibits a change in an optical path length difference of the expanded light along the expansion direction; an image sensor designed to detect the expanded light; and a processing device that is set up to measure a displacement on the measuring surface based on a displacement of a peak position of an interference signal in an image detected by the image sensor.

[0146] According to the above setup, the interference light from the first interferometer produces interference fringes whose phase varies depending on the wavelength, in accordance with the displacement across the measurement surface. Consequently, in the time domain, the interference fringes appear only near a region where the optical path length difference is zero, and no interference fring is observable in other regions because the interference fringes cancel each other out at their respective wavelengths. However, the interference fring can be observed by expanding it with respect to each of the wavelengths. Existing spectral-domain displacement measurement instruments use a spectrometer to expand the interference light with respect to each of the wavelengths in order to detect the interference fring.

[0147] According to the above setup, the interference light emitted by the first interferometer is transmitted through the second interferometer. With respect to the optical path difference at the second interferometer, which is generated in the expanded light, an interference signal peak is produced at a position where the optical path difference becomes equal to twice the displacement of the workpiece. This interference peak is detected as an interference peak on the image of the expanded light. More precisely, the expanded light, which expands in the direction of expansion and exhibits a change in the optical path difference along this direction, can reflect the interference peak, corresponding to the optical path difference of the expanded light, onto the image expanded in the same direction. This enables a highly accurate measurement of the displacement at the measurement surface based on the interference peak on the image.

[0148] According to the above arrangement, since the interference peaks of the expanded light image are measured, even signals that vary continuously along the expansion direction can be measured in a single shot, and the mechanical operations and measurement time required as with existing time-domain displacement instruments are unnecessary. Furthermore, the measurable range can be increased by amplifying the change in the optical path length difference of the expanded light along the expansion direction in the second interferometer.

[0149] According to the above arrangement, the displacement of the measurement area is measured based on the distance between the interference peaks in the expanded light image, allowing for a stable, highly accurate measurement regardless of the presence of error factors (e.g., temperature changes). That is, if components of the displacement measuring instrument are affected by temperature changes, the positions of the interference peaks detected by the image sensor may shift. If the measurement is performed solely using positional information from a single interference peak, the measurement accuracy may be degraded by errors caused by changes in the positional information. However, according to the above arrangement, which determines the distance (i.e.,(relative shift between the two interference peaks) is used, canceling out the error components at the time of calculating the distance, even if the peaks are shifted due to temperature, so that a highly accurate measurement can be carried out constantly and stably. Additional Explanation 2

[0150] The displacement measuring instrument according to Additional Declaration 1, wherein the second interferometer comprises a beam splitter configured to split the interference light and cause the split interference light to fall on the first reflecting surface and the second reflecting surface, the first reflected light and the second reflected light fall onto the image sensor via the beam splitter, and at least one of the first reflective surface or the second reflective surface is an inclined mirror, arranged so that it is inclined in the direction of expansion with respect to an incident optical axis.

[0151] According to the above arrangement, the first interferometer and the second interferometer can each be implemented as a Twyman-Green interferometer. The inclined mirror, which defines one or both of the first and second reflective surfaces, allows the optical path length difference in the direction of the incident optical axis to be generated by the corresponding difference of the surfaces along the inclined direction. This makes it possible to generate expanded light that expands in the predetermined expansion direction and exhibits a change in the optical path length difference along the expansion direction. Additional Explanation 3

[0152] The displacement measuring instrument according to Additional Explanation 2, wherein the inclined mirror is a multi-stage inclined mirror comprising a plurality of inclined mirrors arranged in a direction intersecting the incident optical axis and the expansion direction, the inclined mirrors being offset in a direction of the incident optical axis.

[0153] According to the above arrangement, by sequentially shifting the inclined mirrors at the respective stages in the direction of the optical axis, the optical path length difference in the direction of the optical axis can be increased as a whole of the multi-stage inclined mirror, so that a wide measurable range can be achieved which cannot be obtained by a single inclined mirror. Additional Explanation 4

[0154] The displacement measuring instrument according to Additional Declaration 3, further comprising an aperture diaphragm provided between the image sensor and the beam splitter and configured to regulate the first reflected light and the second reflected light.

[0155] According to the above arrangement, a large depth of field can be achieved by blocking the diffraction light originating from the structure of the multi-stage inclined mirror, so that the reflected light from the multi-stage inclined mirror, which has a large depth in the direction of the optical axis, can be clearly imaged, thereby achieving a larger measurable area. Additional Explanation 5

[0156] The displacement measuring instrument according to Additional Declaration 2, further comprising a cylindrical lens which extends continuously in the direction of expansion and is configured to condense the incident light onto the image sensor.

[0157] According to the above arrangement, the incident light is condensed to increase its intensity when it is received by the image sensor. Additionally, by using the cylindrical lens, which is continuous in the expansion direction, it is possible to ensure properties of the expanded light that are necessary for the measurement (i.e., expansion in the predetermined expansion direction and exhibiting a change in the optical path length difference along the expansion direction). Additional Explanation 6

[0158] The displacement measuring instrument according to Additional Declaration 1, wherein the second interferometer comprises a beam splitter configured to split the interference light and cause the split interference light to fall on the first reflecting surface and the second reflecting surface, the first reflected light and the second reflected light fall on the image sensor without passing through the beam splitter, and The angle of incidence of the first reflected light onto the image sensor differs from the angle of incidence of the second reflected light onto the image sensor.

[0159] According to the above setup, the first interferometer is provided by a Twyman-Green interferometer, and the second interferometer is provided by a dual-beam, one-way interferometer similar to a Mach-Zehnder interferometer. Using the dual-beam, one-way interferometer, whose optical path is simpler than that of the Twyman-Green interferometer, reduces the loss in the amount of light reaching the image sensor.

[0160] In the second interferometer, a continuous optical path length difference can be generated on the expanded light produced on the surface of the image sensor by differentiating the angles of incidence of the first and second reflected light onto the image sensor. In this case, by shaping the image sensor so that it is long in the expansion direction, the optical path length difference in the expanded light can be increased, thereby extending the measurement range. Furthermore, by using a one-dimensional sensor that extends in the expansion direction, similar to the image sensor, the measurement operation can be accelerated even further. Additional Explanation 7

[0161] The displacement measuring instrument according to Additional Explanation 6, in which an optical path length from the beam splitter via the first reflected surface to the image sensor differs from an optical path length from the beam splitter via the second reflected surface to the image sensor.

[0162] According to the above arrangement, the peaks of the interference fring appearing on the expanded light received by the image sensor can be shifted in the expansion direction (i.e., the direction in which the image sensor is elongated) by adjusting the positions of the first and second reflective surfaces to create a difference in the optical path length of the reflected light between the first and second surfaces. For example, by shifting an interference signal peak, which serves as a reference indicating that the optical path difference of the second interferometer is zero, to one end of a light-receiving region, a longer measurement width of the optical path difference can be created, and the measurement range can be extended. Additional Explanation 8

[0163] The displacement measuring instrument according to Additional Declaration 6, further comprising a cylindrical lens which extends continuously in the direction of expansion and is configured to condense the incident light onto the image sensor.

[0164] According to the above arrangement, the incident light is condensed to increase its intensity when it is received by the image sensor. Additionally, by using the cylindrical lens, which is continuous in the expansion direction, it is possible to ensure properties of the expanded light that are necessary for the measurement (i.e., expansion in the predetermined expansion direction and exhibiting a change in the optical path length difference along the expansion direction). Additional Explanation 9

[0165] The displacement measuring instrument according to Additional Declaration 1, in which the entry of the source light and the exit of the interference light are at the same location in the first interferometer, and A path of source light from the light source to the first interferometer and a path of interference light from the first interferometer to the second interferometer are made of optical fibers, and sections of the optical fibers that are near the first interferometer are bundled into a single fiber.

[0166] According to the above arrangement, the first interferometer and the workpiece can be located away from the light source and the second interferometer, so that the size of a probe containing the first interferometer can be reduced, making it possible to easily insert the probe even if the workpiece is located in a narrow gap or the like. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2017-524138 A

[0003] JP 2017-38997 A

[0004] JP 2021-189112 A

[0005]

Claims

[1] Displacement measuring instrument (1, 1A to 1G), comprising: a light source (2) designed to produce broadband source light (L11); a first interferometer (10, 10G) configured to split the source light (L11) into reference light (L12, L13) and measurement light (L14, L15), to cause the reference light (L12, L13) to fall upon a reference surface (13) and the measurement light (L14, L15) to fall upon a measurement surface, and to superimpose the reference light (L12, L13) and the measurement light (L14, L15) reflected from the reference surface (13) or the measurement surface to produce interference light (L16, L21); a second interferometer (20, 20A to 20F) configured to split the interference light (L16, L21), causing the split interference light (L16, L21) to be incident on a first reflecting surface (23) and a second reflecting surface (25), and to superimpose a first reflected light (L23, L26) reflected from the first reflecting surface (23) and a second reflected light (L25, L27) reflected from the second reflecting surface (25) to produce expanded light (L28) which expands in a predetermined expansion direction (E) and exhibits a change in an optical path length difference of the expanded light (L28) along the expansion direction (E); an image sensor (3) configured to detect the expanded light (L28); and a processing device (4) which is configured to measure a displacement on the measuring surface based on a displacement of a peak position of an interference signal in an image detected by the image sensor (3). [2] Displacement measuring instrument (1, 1A to 1C, 1G) according to claim 1, wherein the second interferometer (20, 20A to 20C) comprises a beam splitter (22) which is configured to split the interference light (L16, L21) and to cause the split interference light (L16, L21) to fall on the first reflecting surface (23) and the second reflecting surface (25), the first reflected light (L26) and the second reflected light (L27) fall onto the image sensor (3) via the beam splitter (22), and at least one of the first reflective surface (23) or the second reflective surface (25) is an inclined mirror arranged so that it is inclined in the expansion direction (E) with respect to an incident optical axis. [3] Displacement measuring instrument (1A to 1C) according to claim 2, wherein the inclined mirror is a multi-stage inclined mirror comprising a plurality of inclined mirrors (23A, 23B) arranged in a direction intersecting the incident optical axis and the expansion direction (E), wherein the inclined mirrors are offset in one direction of the incident optical axis. [4] Displacement measuring instrument (1B) according to claim 3, further comprising: an aperture diaphragm (27B) provided between the image sensor (3) and the beam splitter (22) and configured to regulate the first reflected light (L26) and the second reflected light (L27). [5] Displacement measuring instrument (1C) according to claim 2, further comprising: a cylindrical lens (281) which extends continuously in the expansion direction (E) and is designed to condense incident light onto the image sensor (3). [6] Displacement measuring instrument (1D to 1F) according to claim 1, wherein the second interferometer (20D to 20F) includes a beam splitter (22) which is configured to split the interference light (L21) and to cause the split interference light (L21) to fall on the first reflecting surface (23) and the second reflecting surface (25), the first reflected light (L23) and the second reflected light (L25) fall on the image sensor (3) without passing through the beam splitter (22), and The angle of incidence of the first reflected light (L23) onto the image sensor (3) differs from the angle of incidence of the second reflected light (L25) onto the image sensor (3). [7] Displacement measuring instrument (1E, 1F) according to claim 6, wherein an optical path length from the beam splitter (22) via the first reflected surface (23) to the image sensor (3) differs from an optical path length from the beam splitter (22) via the second reflected surface (25) to the image sensor (3). [8] Displacement measuring instrument (1F) according to claim 6, further comprising: a cylindrical lens (28F) which extends continuously in the expansion direction (E) and is designed to condense incident light onto the image sensor (3). [9] Displacement measuring instrument (1G) according to claim 1, wherein an entry of the source light (L11) and an exit of the interference light (L16) at the same location in the first interferometer (10G), and a path of source light (L11) from the light source (2) to the first interferometer (10G) and a path of interference light (L16) from the first interferometer (10G) to the second interferometer (20A) are made of optical fibers (31 to 33), and sections of the optical fibers (31 to 33) that are near the first interferometer (10G) are bundled into a single fiber.

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